1. Field of the Invention
This invention relates to positioning a printing ribbon between the printing mechanism and the medium upon which the printing is to be performed. More specifically, it pertains to a mechanism for maintaining the printing ribbon at a constant slant angle with the horizontal, thereby causing the printing members to strike the ribbon in an oblique line from the bottom to the top of the ribbon, in a non-repetitive manner as the ribbon circulates through the ribbon handler, thereby prolonging the life of the ribbon by spreading the load over a larger area.
2. Description of the Prior Art
Typically, a print ribbon is simply moved horizontally past a printing head thereby presenting exactly the same portion of the ribbon continually to the impact members. This configuration reduces the ribbon life substantially.
More recently, a slant ribbon technique has been employed but without a positive mechanism for providing vertical movement. For example, non-positive gripping slick guides have been used which allow the ribbon to dwell longer at one height than another causing excessive wear and reduced life. Also, rolling cylinders have been provided as ribbon guides for the slant ribbon system. These are highly susceptible to imparting an upward or downward force, driving the ribbon off the guides as a result of small angle variations of the guide journals.
By providing threaded grooves, positive gripping control is achieved and the disadvantages cited above are removed.